Various thermoelastomeric materials have been used in the past to impart desirable heat or cold retaining properties to objects, such as hot and cold compresses and disposable ice packs. Such materials have included, for example, substituted urea/urethane hydrogels. These hydrogels are quite soft and pliable, yet are capable of remaining hot or cold for extened periods of time. Unfortunately, the useful life of such gel containing objects is usually quite short. Further, such prior devices have the gelled material enclosed or confined in a pouch or bag.
The hydrogen material itself generally is prepared by mixing effective amounts of a polyalcohol (polyol) with a diisocyanate-capped prepolymer followed by the addition of water. The mixture is then poured into an appropriate mold where gel formation will occur spontaneouslyin a short period of time. Although much of the carbon dioxide gas which is liberated as a by-product of the water and isocyanate reaction escapes from the mixture prior to gel formation, a froth of carbon dioxide gas interspersed in the gel often remains at the uppermost surface of the gel. This is particularly true when the ratio of the surface area to the volume of the mold used is small. Although this froth does ot seriously impair the qualities of the hydrogel, it is unsightly and less desirable than a gel having a more uniform consistency.
Preparation of objects incorporating the above noted hydrogel material has been most commonly effected by placing the premolded hydrogel material in an envelope or pouch of cloth, plastic or other material and then sealing the open end of the envelope or pouch. The hydrogel material incorporated into objects so prepared, although having the desired thermal efficiency, often slips or shifts within the confines of its compartment because no satisfactory method for adhering the hydrogel to the covering material exists. Placing the formed hydrogel material within the envelope or pouch requires an additional step, and therefore additional cost, in the production of such objects. Further, placing a covering completely around the hydrogel material reduces the therapeutic capability of the gel by insulating it from the skin when in use in hot or cold therapy. A need exists, therefore, for a method of bonding hydrogel materials directly to a covering material. Further, a need exists for a more efficient way of making articles incorporating such hydrogels for hot and cold therapy purposes.